I don’t even know really what intertia means let alone moment of it??
Plz help
In: 6
Inertia is the resistance to a change in motion. If you imagine a car, and a train in front of you, and you want to push them to get them both rolling up to 5 miles an hour, you can imagine it’s easier to do this with the car, than the train. We would say that the train has “a higher inertia” than the car does. Higher inertia means harder to accelerate.
But that’s straight-line motion, what about spinning motion? Here’s where “Moment of Inertia” comes into play. Imagine a basketball and a bowling ball, the same size and the same weight. Both balls have the same “center” of weight (I’m saying weight not mass because this is ELI5), which is just the center of the ball. BUT a bowling is full up of heavy stuff but a basketball is more like heavy, thin outer shell filled with air.
What we’re getting at here is that making the balls spin faster *isn’t* only about the where the center of weight is (it’s the same for both balls), *nor* how much the balls weigh (it’s the same for both balls) BUT you need to include some information about how the weight of the ball is distributed from the center. Since the basketball has all of it’s weight concentrated far from the center, it’s harder to spin vs. the bowling ball that has it’s weight evenly distributed.
A visualization for “why” might be imagine a see-saw. Making a see-saw balance isn’t just based on the weight of the people, but how far they are from the pivot. A small person can balance a big person if the small person is far from the pivot and the big person is right up on it. Similarly, a concentration of mass *far* from the center of the ball has a bigger effect than mass that’s closer to the ball.
In science speak, “Moment” refers to twisting and spinning forces and “inertia” means resistance to motion. So “Moment of Inertia” means an objects resistance to spinning.
Here’s one final parallel that might help. If you’re building a skyscraper, you want your steel beams to resist bending, right? So how do you shape them? Do you just make big steel cylinders? That’s not great because you’re making bowling-ball type shapes, all the weight is concentrated close to the center, you want to make a basketball type shape, put the weight far from the center. So you can make tubes, that would be better, but making round shapes is expensive and they are still pretty big. OR you could make an “I” shaped beam, two big thick heavy metal plates separated as far apart as possible with a thin central flange. That’s the strongest anti-bending shape possible AND is really cheap to make. And that, kids, is why we use I-beams to build buildings and not just hunks of steel or tubes.
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